The present invention belongs to the technical field of a magnetic tape used for DDS (digital data storage), DAT (digital audio tape) and the like. More particularly, the present invention relates to an evaluation reference tape capable of adequately evaluating a sensitivity correction of a dropout testing apparatus and a recording/replaying system of a magnetic tape, a method of manufacturing the evaluation reference tape and an apparatus for manufacturing the evaluation reference tape.
Magnetic tapes used for the DAT or the DDS are basically composed of a base layer which is a film such as PET (polyethylene terephthalate) or the like, a magnetic recording layer formed on one of the surfaces of the base layer, a backing layer formed on the surface of the base layer opposite to the magnetic recording layer for the purposes of improving the stability of the magnetic tape when it is transported and the strength thereof, and the like.
In the magnetic tape having such composition as described above, a defect of the magnetic recording layer derived from a scar or the like will cause a phenomenon such as a decrease of recording magnetic power or output, a recording or replaying error and is commonly called as dropout.
Therefore, in the magnetic tape, it is ideal that there is no dropout, however, the dropout is intrinsically unavoidable in the magnetic tape. For this reason, a dropout testing apparatus is employed at the time of manufacturing the magnetic tape to measure the number of the dropout which has exceeded a predetermined threshold value of at least one of output decrease and time length and, if the thus measured number exceeds, to judge the magnetic tape to be inappropriate or NG (no good) as a product.
In the case of DAT cartridges, there are many cases in which actual drives (recording/replaying apparatuses) are remodeled and then used as the dropout testing apparatuses. The threshold of the number of the dropout differs from tape to tape in accordance with the type thereof.
In order to appropriately execute the above-described dropout testing, it is necessary that the dropout testing apparatus should correctly measure the number of the dropout which exceeds the predetermined value so that sensitivity of the dropout testing apparatus should be appropriately set.
Therefore, in manufacturing of the magnetic tape, the magnetic tape which serves as reference, namely, an evaluation reference tape (hereinafter referred to simply as “reference tape”) is manufactured so that it is put to use in sensitivity correction (calibration) of the dropout testing apparatus.
On the other hand, such a reference tape is not capable of knowing how large and deep a defect actually is on a magnetic recording layer.
There can only be known how large and deep the defect is by analyzing the magnetic tape. However, since it is essential that such analysis requires observation using an electron microscope or magnetic phenomenon, the thus analyzed magnetic tape results in being destroyed and no more applicable as a reference tape; therefore, such analysis is ordinarily performed on a part of the magnetic tape.
For the above-described reason, at present, sensitivity correction of the dropout testing apparatus can not be performed in accordance with the depth or size of the defect in the reference tape so that, in the dropout testing, correspondence between the dropout and the depth and size of the defect is vague; as a result, good quality control can not be performed.